Tips for the garden this week

Dahlia tubers

If the weather’s settled and your dahlias have good shoots, they could go out now. Whether you plant in a specific dahlia border or simply dot them about your flowerbeds, they all like a humus-rich soil. Dig in compost or leaf mould before planting and try to avoid using fertilisers rich in nitrogen on dahlias (or any other flowering plants). You’ll then avoid soft stems that can be vulnerable to wind damage.

Cannas

Exotic-looking cannas are, in fact, quite easy to grow. They should be ready to plant out now. A light, humus-rich soil is best.When the cold of autumn arrives, lift them and pot up with a good compost, store them in a cold greenhouse and keep them moist.

Cucumbers

Unheated greenhouses should now be warm enough to set cucumber plants. Although they need more humid growing conditions than tomatoes, they’re invariably reared together. Grow them exactly as you do your tomatoes. The only difference is that, when they’re growing, they must be trained and regularly tied to a frame, which can be somewhat time-consuming.

Potatoes

If you were able to get your potatoes planted in April, they could now be at a stage to earth up. When the haulms (leafy stems) are about 9in tall, we find the draw hoe to be the best tool to pull up the soil between the stems to make a hill or ridge leave just the growing tip showing. For ease of hilling, keep the ground between the rows well cultivated and weed-free. Blight can be a serious problem in summer, especially if it’s wet and warm. Keep a lookout for the first signs: brown blotches on the leaves. There’s no effective organic control for blight, so if you have it, remove the damaged leaves. In extreme cases, cut the stems down to the ground to stop it getting to the tubers.

Turnips

Memories of the large woody roots harvested in the autumn may have put gardeners and cooks off growing turnips. However, if you sow them at intervals from March to May, you can dig them up when they reach the size of golf balls and use them raw in salads, or cook them when they’re no larger than tennis balls.

Sow seeds direct in drills outside and, once germinated, thin seedlings to 3in apart for fresh use and 9in for winter use. If flea beetles visit your garden, you’ll have to protect the crop. Derris Dust used to be the organic solution to the problem of flea beetle, but it’s been withdrawn from the market and should no longer be on sale. We shall experiment this year with covering the drills with fleece and removing them when the seedlings have developed two or three true leaves. We hope this will get the seedlings through their most vulnerable period.

Swedes

Although closely related to turnips, swedes need longer to grow. Sown now and protected in the same way as turnips, they’ll be ready from autumn to spring. Seedlings must be thinned to 9in apart.

Philip Maddison is head gardener at Harrington Hall, Lincolnshire (www.harringtonhallgardens.co.uk)